Optimizing power transfer to negative pressure sources in negative pressure therapy systems

ABSTRACT

Embodiments of negative pressure wound therapy systems and methods are disclosed. In one embodiment, an apparatus includes a driving circuit that supplies a driving signal to a negative pressure source to cause the negative pressure source to provide negative pressure via a fluid flow path to a wound dressing. The apparatus furthers include a controller that adjusts a frequency of the driving signal supplied by the driving circuit according to a comparison of a previous magnitude and a subsequent magnitude of the driving signal while the negative pressure source provides negative pressure. The transfer of power to the negative pressure source can thereby be tuned to maximize an amount of power transferred to the negative pressure source.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 62/331,098, filed May 3, 2016, and U.S. Provisional Application No. 62/479,588, filed Mar. 31, 2017; the disclosures of which are hereby incorporated by reference in their entirety.

BACKGROUND

Embodiments of the present disclosure relate to methods and apparatuses for dressing and treating a wound with negative or reduced pressure therapy or topical negative pressure (TNP) therapy. In particular, but without limitation, embodiments disclosed herein relate to negative pressure therapy devices, methods for controlling the operation of TNP systems, and methods of using TNP systems.

SUMMARY

In some embodiments, an apparatus for applying negative pressure to a wound, the apparatus can include a source of negative pressure, a driving circuit, and a controller. The source of negative pressure can provide negative pressure via a fluid flow path to a wound dressing. The driving circuit can supply a driving signal to the source of negative pressure to cause the source of negative pressure to provide negative pressure. The driving signal can have a driving signal magnitude and a driving signal frequency. The controller can, while the source of negative pressure is maintaining negative pressure under the wound dressing within a pressure range, iteratively and at an operating frequency: determine the driving signal magnitude detected at a first time and the driving signal magnitude detected at a second time subsequent to the first time, compare the driving signal magnitude detected at the first time and the driving signal magnitude detected at the second time, in response to the driving signal magnitude detected at the first time being less than the driving signal magnitude detected at the second time, operate the driving circuit to increase the driving signal frequency, and in response to the driving signal magnitude detected at the first time being greater than the driving signal magnitude detected at the second time, operate the driving circuit to decrease the driving signal frequency.

The apparatus of the preceding paragraph can include one or more of the following features: The controller can to operate the driving circuit so that the driving signal frequency matches an initial frequency when the driving circuit activates the source of negative pressure to begin providing negative pressure, and the controller can operate the driving circuit to increase or decrease the driving signal frequency within a first period of time following the driving circuit activating the source of negative pressure. The source of negative pressure can have a mechanical resonance frequency, and the mechanical resonance frequency can be greater than the initial frequency. The source of negative pressure can have a mechanical resonance frequency, and the mechanical resonance frequency can be less than the initial frequency. The mechanical resonance frequency can be between 5 kHz and 100 kHz. The first period of time can be between 1 msec and 1 min. The driving signal magnitude detected at the second time in a first iteration can be used as the driving signal magnitude detected at the first time in a second iteration subsequent to the first iteration. The first iteration and the second iteration may not be separated by another iteration. The controller can: operate the driving circuit to increase the driving signal frequency by a first amount; and operate the driving circuit to decrease the driving signal frequency by a second amount. The first amount can be the same as the second amount. The first amount can be different from the second amount. The first amount or the second amount can vary over time. The first amount or the second amount can be constant over a second period of time while the source of negative pressure is maintaining negative pressure under the wound dressing within the pressure range. The second period of time can be between 10 sec and 10 min. The first amount or the second amount can be between 1 Hz and 1000 Hz. The operating frequency can vary over time. The operating frequency can be constant over a third period of time while the source of negative pressure is maintaining negative pressure under the wound dressing within the pressure range. The third period of time can be between 10 sec and 10 min. The operating frequency can be between 0.1 Hz and 100 Hz. The source of negative pressure can include a piezoelectric pump. The source of negative pressure can include a micropump. The source of negative pressure can perform negative pressure wound therapy when negative pressure under the wound dressing is maintained within the pressure range. The apparatus can further include the wound dressing, and the source of negative pressure can be disposed on or within the wound dressing. The driving circuit can include an H-bridge circuit. The controller can further provide a control signal to the driving circuit, and the controller can control the driving signal by adjusting a pulse width modulation of the control signal. The driving circuit can supply the driving signal by supplying an electrical voltage across input terminals of the source of negative pressure via the coupling circuit, and the electrical voltage can range from greater than −50 V to less than +50 V. The driving signal can include an electrical current.

A method of operating, using, or manufacturing the apparatus of the preceding two paragraphs is also disclosed.

In some embodiments, a method of operating a negative pressure wound therapy apparatus is disclosed. The method can include: supplying a driving signal at a first time and at a second time to a source of negative pressure, the driving signal having a driving signal magnitude and a driving signal frequency, the second time being subsequent to the first time; providing negative pressure via a fluid flow path to a wound dressing with the source of negative pressure responsive to the driving signal; determining the driving signal magnitude at the first time and the driving signal magnitude at the second time; comparing the driving signal magnitude at the first time and the driving signal magnitude at the second time; in response to the driving signal magnitude at the first time being less than the driving signal magnitude at the second time, increasing the driving signal frequency supplied to the source of negative pressure; and in response to the driving signal magnitude at the first time being greater than the driving signal magnitude at the second time, decreasing the driving signal frequency supplied to the source of negative pressure.

The method of the preceding paragraph can include one or more of the following features: The increasing the driving signal frequency can include increasing the driving signal frequency by a first amount; and the decreasing the driving signal frequency can include decreasing the driving signal frequency by a second amount. The first amount can be the same as the second amount. The first amount can be different from the second amount. The first amount or the second amount can be between 1 Hz and 1000 Hz. The source of negative pressure can include a piezoelectric pump. The source of negative pressure can include a micropump. The driving signal can include an electrical current.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the present disclosure will be apparent from the following detailed description, taken in conjunction with the accompanying drawings of which:

FIG. 1 illustrates a negative pressure therapy system according to some embodiments.

FIGS. 2A and 2B respectively illustrate a side view and top view of a negative pressure therapy system according to some embodiments, such as the negative pressure therapy system of FIG. 1.

FIG. 3 illustrates a block diagram of electrical communication paths between a power source, control circuitry, and negative pressure source, as well as components of the control circuitry, according to some embodiments.

FIGS. 4A and 4B illustrate simplified circuit components of a driving circuit according to some embodiments.

FIG. 4C illustrates circuit components of a driving circuit according to some embodiments.

FIG. 5 illustrates circuit components of a coupling circuit according to some embodiments.

FIG. 6 illustrates a therapy control process performable by a negative pressure therapy system according to some embodiments.

DETAILED DESCRIPTION

The present disclosure relates to methods and apparatuses for dressing and treating a wound with reduced pressure therapy or topical negative pressure (TNP) therapy. In particular, but without limitation, embodiments of this disclosure relate to negative pressure therapy apparatuses, methods far controlling the operation of TNP systems, and methods of using TNP systems. The methods and apparatuses can incorporate or implement any combination of the features described below.

Many different types of wound dressings are known for aiding in the healing process of a human or animal. These different types of wound dressings include many different types of materials and layers, for example, gauze, pads, foam pads or multi-layer wound dressings. TNP therapy, sometimes referred to as vacuum assisted closure, negative pressure wound therapy, or reduced pressure wound therapy, can be a beneficial mechanism for improving the healing rate of a wound. Such therapy is applicable to a broad range of wounds such as incisional wounds, open wounds and abdominal wounds or the like.

TNP therapy can assist in the closure and healing of wounds by reducing tissue oedema, encouraging blood flow, stimulating the formation of granulation tissue, removing excess exudates, and reducing bacterial load and thus, infection to the wound. Furthermore, TNP therapy can permit less outside disturbance of the wound and promote more rapid healing.

As is used herein, reduced or negative pressure levels, such as −X mmHg, represent pressure levels that are below atmospheric pressure, which typically corresponds to 760 mmHg (or 1 atm, 29.93 inHg, 101.325 kPa, 14.696 psi, etc.). Accordingly, a negative pressure value of −X mmHg reflects pressure that is X mmHg below atmospheric pressure, such as a pressure of (760−X) mmHg. In addition, negative pressure that is “less” or “smaller” than −X mmHg corresponds to pressure that is closer to atmospheric pressure (e.g., −40 mmHg is less than −60 mmHg). Negative pressure that is “more” or “greater” than −X mmHg corresponds to pressure that is further from atmospheric pressure (e.g., −80 mmHg is more than −60 mmHg).

Overview

Control circuitry of a TNP apparatus can supply a driving signal (for example, an electrical current) to a negative pressure source and vary a frequency of the driving signal (for instance, an AC waveform frequency of the electrical current). By varying the frequency over time (for example, to match a mechanical resonance frequency of a piezoelectric pump of the negative pressure source), the control circuitry can tune the transfer of power to the negative pressure source to maximize an amount of power transferred to the negative pressure source. As a result, the TNP apparatus can automatically accommodate for component variances attributable to, for example, operating temperatures or manufacturing differences and operate the negative pressure source at an optimum or near optimum power level. In some implementations, the resonance frequency of the negative pressure source can vary in response to, for example, variations in temperature, humidity, and the like.

Reduced Pressure Therapy Systems and Methods

FIG. 1 illustrates a negative pressure therapy system 100 that includes a TNP apparatus 11 and a wound 14. The TNP apparatus 11 can be used to treat the wound 14. The TNP apparatus 11 can include control circuitry 12A, memory 12B, a negative pressure source 12C, a user interface 12D, a power source 12E, a first pressure sensor 12F, and a second pressure sensor 12G that are configured to electrically communicate with one another. In addition, the TNP apparatus 11 can include a wound dressing 13. The power source 12E can provide power to one or more components of the TNP apparatus 11.

One or more of the control circuitry 12A, memory device 12B, negative pressure source 12C, user interface 12D, power source 12E, first pressure sensor 12F, and second pressure sensor 12G can be integral with, incorporated as part of, attached to, or disposed in the wound dressing 13. The TNP apparatus 11 can accordingly be considered to have its control electronics and pump on-board the wound dressing 13 rather than separate from the wound dressing 13.

The control circuitry 12A can include one or more controllers (for example, a microcontroller or microprocessor), activation circuits, boost converters, current limiters, feedback conditioning circuits, and H-bridge inverters. The control circuitry 12A can control the operations of one or more other components of the TNP apparatus 11 according at least to instructions stored in the memory device 12B. The control circuitry 12A can, for instance, control operations of and supply of negative pressure by the negative pressure source 12C.

The negative pressure source 12C can include a pump, such as, without limitation, a rotary diaphragm pump or other diaphragm pump, a piezoelectric pump, a peristaltic pump, a piston pump, a rotary vane pump, a liquid ring pump, a scroll pump, a pump operated by a piezoelectric transducer, or any other suitable pump or micropump or any combinations of the foregoing. The pump can include an actuator driven by a source of energy, such as electrical energy, mechanical energy, and the like. For example, the actuator can be an electric motor, a piezoelectric transducer, a voice coil actuator, an electroactive polymer, a shape-memory alloy, a comb drive, a hydraulic motor, a pneumatic actuator, a screw jack, a servomechanism, a solenoid actuator, a stepper motor, a plunger, a combustion engine, and the like. In some embodiments, the negative pressure source 12C can supply negative pressure by converting electrical energy to mechanical energy without converting the electrical energy to magnetic energy. In such embodiments, the pump can have a different impact when electrically coupled to one or more other components of the control circuitry 12A than if the negative pressure source 12C supplied negative pressure by converting the electrical energy to the magnetic energy and then to the mechanical energy.

The user interface 12D can include one or more elements that receive user inputs or provide user outputs to a patient or caregiver. The one or more elements that receive user inputs can include buttons, switches, dials, touch screens, or the like, and the one or more elements that provide user outputs can include activation of a light emitting diode (LED) or one or more pixels of the display or activation of a speaker or the like. In one example, the user interface 12D can include a switch to receive user inputs (for instance, a negative pressure activation or deactivation input) and two LEDs to indicate an operating status (for example, functioning normally, under fault condition, or awaiting user input) of the TNP apparatus 11.

The first pressure sensor 12F can be used to monitor pressure underneath the wound dressing 13, such as pressure in a fluid flow path connecting the negative pressure source 12C and the wound 14, pressure at the wound 14, or pressure in the negative pressure source 12C. The second pressure sensor 12G can be used to monitor pressure external to the wound dressing 13. The pressure external to the wound dressing can be atmospheric pressure; however, the atmospheric pressure can vary depending on, for instance, an altitude of use or pressurized environment in which the TNP apparatus 11 may be used.

The control circuitry 12A can control the supply of negative pressure by the negative pressure source 12C according at least to a comparison between the pressure monitored by the first pressure sensor 12F and the pressure monitored by the second pressure sensor 12G.

The wound dressing 13 can include a wound contact layer, a spacer layer, and an absorbent layer. The wound contact layer can be in contact with the wound 14. The wound contact layer can include an adhesive on the patient facing side for securing the dressing to the skin surrounding the wound 14 or on the top side for securing the wound contact layer to a cover layer or other layer of the wound dressing 13. In operation, the wound contact layer can provide unidirectional flow so as to facilitate removal of exudate from the wound while blocking or substantially preventing exudate from returning to the wound 14. The spacer layer can assist in distributing negative pressure over the wound site and facilitating transport of wound exudate and fluids into the wound dressing 13. Further, the absorbent layer can absorb and retain exudate aspirated from the wound 14.

The control circuitry 12A can monitor the activity of the negative pressure source 12C, which may include monitoring a duty cycle of the negative pressure source 12C (for example, the duty cycle of the actuator of the negative pressure source). As is used herein, the “duty cycle” can reflect the amount of time the negative pressure source 12C is active or running over a period of time. In other words, the duty cycle can reflect time that the negative pressure source 12C is in an active state as a fraction of total time under consideration. Duty cycle measurements can reflect a level of activity of the negative pressure source 12C. For example, the duty cycle can indicate that the negative pressure source 12C is operating normally, working hard, working extremely hard, etc. Moreover, the duty cycle measurements, such as periodic duty cycle measurements, can reflect various operating conditions, such as presence or severity of leaks, rate of flow of fluid (for instance, air, liquid, or solid exudate, etc.) aspirated from a wound, or the like. Based on the duty cycle measurements, such as by comparing the measured duty cycle with a set of thresholds (for instance, determined in calibration), the controller can execute or be programmed to execute algorithms or logic that control the operation of the system. For example, duty cycle measurements can indicate presence of a high leak, and the control circuitry 12A can be programmed to indicate this condition to a user (for instance, patient, caregiver, or physician) or temporarily suspend or pause operation of the source of negative pressure in order to conserve power.

When the TNP apparatus 11 may be used to treat the wound 14, the wound dressing 13 can create a substantially sealed or closed space around the wound 13 and under the wound dressing 13, and the first pressure sensor 12F can periodically or continuously measure or monitor a level of pressure in this space. The control circuitry 12A can control the level of pressure in the space between a first negative pressure set point limit and at least a second negative pressure set point limit. In some instances, the first set point limit can be approximately −70 mmHg, or from approximately −60 mmHg or less to approximately −80 mmHg or more. In some instances, the second set point limit can be approximately −90 mmHg, or from approximately −80 mmHg or less to approximately −100 mmHg or more.

FIG. 2A illustrates a side view of a negative pressure therapy system 200, and FIG. 2B illustrates a top view of the negative pressure therapy system 200. The negative pressure therapy system 200 can be an example implementation of the negative pressure therapy system 100.

In the negative pressure therapy system 200, the wound dressing 13 of the TNP apparatus 11 is shown as attached to the wound 14. Arrows depict the flow of air through the wound dressing 13 and wound exudate from the wound 14. The TNP apparatus 11 can include an air exhaust 26 and a component area 25, such as a components housing or storage area for components of the TNP apparatus 11 like one or more of the control circuitry 12A, memory device 12B, negative pressure source 12C, user interface 12D, power source 12E, first pressure sensor 12F, and second pressure sensor 12G.

The user interface 12D of the negative pressure therapy system 200 can include a switch 21 (such as a dome switch), a first indicator 23 (such as a first LED), and a second indicator 24 (such as a second LED). The switch 21 can receive a negative pressure activation or deactivation user input (for example, such as receiving the activation or deactivation user input in response to depression of the switch 21 for a period of time, like from between 0.5 seconds and 5 seconds). The first indicator 23 and the second indicator 24 can indicate an operating status like functioning normally, under fault condition, or awaiting user input. In some implementations, the switch 21 can couple to a power supply connection of the negative pressure source 12C or the control circuitry 12A or an enable signal of the negative pressure source 12C or the control circuitry 12A to activate or deactivate supply of negative pressure or disable supply of negative pressure.

Component parts of the wound dressing 13 of the negative pressure therapy system 200 are illustrated to include an airlock layer 27, an absorbing layer 28, and a contact layer 29. The airlock layer 27 can enable air flow. The absorbing layer 28 can absorb wound exudate. The contact layer 29 can be soft and include silicon and be used to couple the TNP apparatus 11 to the patient.

FIG. 3 illustrates a block diagram 300 depicting example electrical communication paths between the power source 12D, control circuitry 12A, and negative pressure source 12C, as well as example components of the control circuitry 12A including a controller 31, a current limiter 32, a driving circuit 33, a feedback conditioner 34, and the coupling circuit 35. FIG. 3 shows, in particular, how the controller 31 can be used to control the supply of negative pressure by the negative pressure source 12C.

The power source 12D can include one or more power supplies, such as batteries (such as, multiple 3 V batteries) or a connection to mains power, to provide power for one or more components of the TNP apparatus 11. The power source 12D can, for instance, provide electrical current and voltage to the current limiter 32. The voltage output by the power source 12D can be around 30 V, such as 29 V±1 V, in some implementations. The power source 12D can additionally include circuitry, such as a boost converter, to control the electrical current and voltage provided to the current limiter 32.

The current limiter 32 can serve to limit or clamp the current at a maximum current level, such as at 100 mA, 250 mA, 466 mA, 500 mA, or 1 A, to limit potential fault current through the driving circuit 33 and the negative pressure source 12C. Under normal operation (for example, in most or some instances), the current limiter 32 may not operate to limit current or voltage.

The current limiter 32 can provide electric current and voltage to the driving circuit 33. The driving circuit 33 can include an H-bridge circuit composed of multiple switches. The H-bridge can be constructed to operate as an H-bridge inverter. The driving circuit 33 can provide feedback to the controller 31 via the feedback conditioner 34. The feedback conditioner 34 can be used, for instance, to condition current feedback information from the driving circuit 33 before the current feedback information is provided to the controller 31. In one example, the feedback conditioner 34 can include a low-pass filter (which can, for example, include active circuit components) to filter switching noise caused by the switching of one or more switches of the driving circuit 33. The controller 31 can, in turn, control the operations of the driving circuit 33 based on the feedback, in some instances.

The controller 31 can control operations of the driving circuit 33, and in turn the negative pressure source 12C, by outputting one or more control signals via one or more outputs of the controller 31 to one or more inputs of the driving circuit 33. For example, the controller 31 can output a first control signal via a first output O1 of the controller 31 to a first input l1 of the driving circuit 33 and a second control signal via a second output O2 of the controller 31 to a second input l2 of the driving circuit 33. The controller 31 can vary a pulse width modulation (PWM) of the first and second control signals to adjust an electrical current and voltage provided by the driving circuit 33 to the coupling circuit 35 and then to the negative pressure source 12C. In one implementation, the driving circuit 33 can include an H-bridge, and the controller 31 can generate the first and second control signals to cause the H-bridge to output electrical currents and voltages having a square waveform (such as about ±30 V) with a frequency (such as 18 kHz to 24 kHz or about 21 kHz) and a duty cycle or ratio (such as about 50%) via a first output O1 of the driving circuit 33 and a second output O2 of the driving circuit 33.

The driving circuit 33 can control supply negative pressure by the negative pressure source 12C by providing electrical currents and voltages to the negative pressure source 12C (for example, to the actuator of the negative pressure source 12C) via the coupling circuit 35. The driving circuit 33 can, for instance, output electrical currents via the first and second outputs O1 and O2 of the driving circuit 33 to a first input l1 of the coupling circuit 35 and a second input l2 of the coupling circuit 35. The coupling circuit 35 can, in turn, output electrical currents via a first output O1 of the coupling circuit 35 and a second output O2 of the coupling circuit 35 to a first input H of the negative pressure source 12C and a second input l2 of the negative pressure source 12C. The electrical currents output by the driving circuit 33 and the coupling circuit 35 can notably be considered to result in positive charge flowing away from the driving circuit 33 (that is, sourcing of electrical current by the driving circuit 33) or toward the driving circuit 33 (that is, sinking of electrical current by the driving circuit 33).

The coupling circuit 35 can serve to limit a rate of change over time of the current supplied by the driving circuit 33 to the negative pressure source 12C or limit a rate of change over time of a voltage across first and second inputs l1 and l2 of the negative pressure source 12C. The coupling circuit 35 can have an inductive reactance greater than 1 mΩ, 5 mΩ, 10 mΩ, 50 mΩ, 100 mΩ, 500 mΩ, 750 mΩ at an operating frequency of 1 kHz. In some embodiments, the coupling circuit 35 can include passive circuit elements and not include active circuit elements, but in other embodiments, the coupling circuit 35 can include one or bath of passive circuit elements and active circuit elements.

FIGS. 4A and 4B illustrate example simplified circuit components of the driving circuit 33. As can be seen from FIGS. 4A and 4B, the driving circuit 33 can be composed of at least four switches, including a first switch S1, a second switch S2, a third switch S3, and a fourth switch S4 but together form an H-bridge. The first and fourth switches S1 and S4 can be closed at the same time and the second and third switches S2 and S3 can be opened at the same time, as shown in FIG. 4A, to supply a first current i1 in a first direction through the coupling circuit 35 and the negative pressure source 12C. The second and third switches S2 and S3 can be closed at the same time and the first and fourth switches S1 and 34 can be opened at the same time, as shown in FIG. 4B, to supply a second current i2 in a second direction through the coupling circuit 35 and the negative pressure source 12C. The first direction can be opposite the second direction.

FIG. 4C illustrates example circuit components of the driving circuit 33 (an H-bridge in the illustrated example) that include a resistor 42. In the example circuit components shown in FIG. 4C, the electrical current that travels through the resistor 42 can be the same or substantially the same as the electrical current that travels through the coupling circuit 35 and the negative pressure source 12C (for example, the actuator of the negative pressure source 12C). As a result, a feedback provided to the feedback conditioner 34 can, for instance, be a voltage level or drop across the resistor 42, which can be proportional to the electrical current that travels through the resistor 42, as well as the electrical current that travels through the coupling circuit 35 and the negative pressure source 12C. Resistor 42 thus can be used to measure one or more properties of the electrical current, such as a magnitude, that is fed to the negative pressure source 12C via the coupling circuit 35, such as via an inductor of the coupling circuit 35 like an inductor 52 described with respect to FIG. 5. The resistor 42 can be coupled to a low-pass filter, as described herein.

FIG. 5 illustrates example circuit components of the coupling circuit 35. As can be seen from FIG. 5, the coupling circuit 35 can include the inductor 52 electrically coupled in series between the first output O1 of the driving circuit 33 and the first input l1 of the negative pressure source 12C, and a wire or an electrical short 54 electrically coupled in series between the second output O2 of the driving circuit 33 and the second input l2 of the negative pressure source 12C. The inductor 52 can have an inductance ranging from 0.1 μH to 1000 μH, 1 μH to 100 μH, or 3 μH to 10 μH, or an inductance of about 7.5 μH. The inductor 52 can have a maximum current rating of greater than 0.25 A, 0.5 A, 0.75 A, 1 A, or 1.25 A. The inductor 52 can be used to oppose rapid changes in a voltage or current supplied to drive the negative pressure source 12C.

In another embodiment, the coupling circuit 35 can include a first wire or a first electrical short electrically coupled in series between the first output O1 of the driving circuit 33 and the first input l1 of the negative pressure source 12C and a second wire or a second electrical short electrically coupled in series between the second output O2 of the driving circuit 33 and the second input l2 of the negative pressure source 12C.

In yet another embodiment, the coupling circuit 35 can include a first wire or a first electrical short electrically coupled in series between the first output O1 of the driving circuit 33 and the first input l1 of the negative pressure source 12C, and an inductor (such as the inductor 52) electrically coupled in series between the second output O2 of the driving circuit 33 and the second input l2 of the negative pressure source 12C.

In yet a further embodiment, the coupling circuit 35 can include a first inductor (such as the inductor 523 electrically coupled in series between the first output O1 of the driving circuit 33 and the first input l1 of the negative pressure source 12C, and a second inductor (such as the inductor 52) electrically coupled in series between the second output O2 of the driving circuit 33 and the second input l2 of the negative pressure source 12C.

In certain implementations, one or more active elements can be used in place of or in addition to one or more inductors.

FIG. 6 illustrates a therapy control process 600 performable by an apparatus, such as the TNP apparatus 11. For convenience, the therapy control process 600 is described in the context of the TNP apparatus 11, but may instead be implemented in other systems described herein or by other computing systems not shown. The therapy control process 600 can be an iterative process by which a TNP apparatus tunes the transfer of power (for example, by adjusting parameters of a driving signal) to a negative pressure source to maximize an amount of power transferred to the negative pressure source and thereby improve the efficiency (which, for example, can be measured by a more efficient power consumption).

The therapy control process 600 may begin within a period of time after startup of the TNP apparatus, such as within 0.001, 0.01, 0.1, 0.5, 1, 2, or 5 minutes of starting supply of pressure with the negative pressure source. The therapy control process 600 can initiate with a particular driving signal energy having an initial magnitude and an initial frequency (for example, an electrical current having an initial current magnitude and an initial current frequency) already being provided to negative pressure source. The initial frequency can be less than or greater than a mechanical resonant frequency (for example, which can be 1, 5, 10, 25, 50, 100, 200, 500, and 1000 kHz) of the negative pressure source.

At block 61, the therapy control process 600 can determine a current magnitude of an electrical current at a previous time and at a next time. For example, the controller 31 can determine a current magnitude of an electrical current supplied by the driving circuit 33 to the coupling circuit 35 and the negative pressure source 12C at a previous time and at a next time. The previous time can be a time prior to the next time. The previous time can, for instance, be a time during an immediately previous iteration to the next time or a time during two or more iterations previous to the next time. The controller 31 can determine the current magnitude (or a value indicative thereof) from the feedback provided by the feedback conditioner 34.

At block 62, the therapy control process 600 can compare the current magnitude at the previous time and the next time. For example, the controller 31 can compare the current magnitude of the electrical current supplied by the driving circuit 33 at the previous time and the current magnitude of the electrical current supplied by the driving circuit 33 at the next time.

At block 63, the therapy control process 600 can determine if the current magnitude at the previous time is less than at the next time. For example, the controller 31 can determine if the current magnitude of the electrical current supplied by the driving circuit 33 at the previous time is less than the current magnitude of the electrical current supplied by the driving circuit 33 at the next time.

If the result at block 63 is yes, the therapy control process 600 can at block 64 increase a current frequency of the electrical current. For example, the controller 31 can increase the frequency of the electrical current supplied by the driving circuit 33 by an increase amount (for example, 1, 3, 5, 10, 30, 50, 70, 100, 200, 300, 500, 700, 850, 1000, 2000, or 5000 Hz). If the result at block 63 is no, the therapy control process 600 can at block 65 decrease a current frequency of the electrical current. For example, the controller 31 can at block 65 decrease the frequency of the electrical current supplied by the driving circuit 33 by a decrease amount (for example, 1, 3, 5, 10, 30, 50, 70, 100, 200, 300, 500, 700, 850, 1000, 2000, or 5000 Hz). The increase amount and decrease amount can be the same or different from one another in some instances or implementations. Moreover, the increase amount or decrease amount can vary over time or be constant for a period of time (for example, 1, 3, 10, 30, or 60 seconds or 1, 3, 5, 10, or 30 minutes).

At block 66, the therapy control process 600 can determine whether to return to block 61 or end. For example, the controller 31 can determine whether to repeat the therapy control process 600, such as by repeating the therapy control process 600 with a repeat frequency (for example, that may be 0.01, 0.03, 0.1, 0.3, 0.5, 1, 3, 5, 10, 30, 50, 100, 300, 500, 1000, 3000, or 5000 Hz and vary or be constant over a period of time, such as 1, 3, 10, 30, or 60 seconds or 1, 3, 5, 10, or 30 minutes) or in response to a triggering event (such as a detected change in temperate of the TNP apparatus measured by a temperature sensor).

Through the therapy control process 600, a mechanical resonant frequency of the negative pressure source can be “searched” (for instance, continuously or periodically) during provision of therapy by attempting to adjust the initial frequency to more closely match the mechanical resonant frequency. The mechanical resonant frequency thus may not be known in advance of operating the TNP apparatus or known with a high precision or accuracy, and yet the frequency of the energy provided to the negative pressure source can be made to substantially match the mechanical resonant frequency. Moreover, the frequency of the energy provided to the negative pressure source can be made to follow the mechanical resonant frequency as the mechanical resonant frequency may change due to the changing operating conditions, which in the case of the negative pressure source being mounted on or within the wound dressing can include a changing temperature, duration of operation, humidity, or the like.

In some embodiments, an apparatus for applying negative pressure to a wound includes a source of negative pressure, a driving circuit, a sensor, and a controller. The source of negative pressure can provide negative pressure via a fluid flow path to a wound dressing placed over the wound. The driving circuit can supply an electrical current to the source of negative pressure to cause the source of negative pressure to provide negative pressure. The electrical current can have a current magnitude and a current frequency. The sensor can detect the current magnitude. The controller can, while the source of negative pressure is providing negative pressure to the wound dressing, iteratively and at a first operating frequency: determine the current magnitude detected at a previous time and the current magnitude detected at a next time subsequent to the previous time; compare the current magnitude detected at the previous time and the current magnitude detected at the next time; in response to the current magnitude detected at the previous time being less than the current magnitude detected at the next time, operate the driving circuit to increase (or decrease) the current frequency; and in response to the current magnitude detected at the previous time being greater than the current magnitude detected at the next time, operate the driving circuit to decrease (or increase) the current frequency.

The apparatus of the preceding paragraph can include one or more of the following features: The controller can operate the driving circuit so that the current frequency matches an initial frequency when the driving circuit activates the source of negative pressure to begin providing negative pressure, and the controller can operate the driving circuit to increase or decrease the current frequency within a first period of time from the driving circuit activating the source of negative pressure. The source of negative pressure can have a mechanical resonance frequency, and the mechanical resonance frequency can be greater than the initial frequency. The source of negative pressure can have a mechanical resonance frequency, and the mechanical resonance frequency can be less than the initial frequency. The source of negative pressure can have a mechanical resonance frequency with one or more subharmonic or harmonic frequencies, and the controller can operate the driving circuit to increase or decrease the current frequency so that the current frequency is not one of the one or more subharmonic or harmonic frequencies or remains outside of one or more frequency ranges that include the one or more subharmonic or harmonic frequencies. The mechanical resonance frequency can be between 5 KHz and 100 kHz, such as around 20 KHz, 22 kHz, or 24 kHz or greater or less than 5 KHz and 100 kHz. The first period of time can be between 1 msec and 1 min, such as around 1 msec, 10 msec, 100 msec, or 1 sec or greater or less than 1 msec and 1 min. The current magnitude detected at the next time in a first iteration is the current magnitude detected at the previous time in a second iteration subsequent to the first iteration. The first iteration and the second iteration may not be separated by another iteration. The controller can: operate the driving circuit to increase the current frequency by a first amount; and operate the driving circuit to decrease the current frequency by a second amount. The first amount can be the same as the second amount. The first amount can be different from the second amount. The first amount or the second amount can vary over time. The first amount or the second amount can be constant over a second period of time while the source of negative pressure is providing negative pressure to the wound dressing. The second period of time can be between 10 sec and 10 min, such as around 10 sec, 1 min, or 10 min or greater or less than 10 sec and 10 min. The first amount or the second amount can be between 1 Hz and 1000 Hz, such as around 1 Hz, 10 Hz, 100 Hz, or 1000 Hz or greater or less than 1 Hz and 1000 Hz. The first operating frequency can vary over time. The first operating frequency can be constant over a third period of time while the source of negative pressure is providing negative pressure to the wound dressing. The third period of time can be between 10 sec and 10 min, such as around 10 sec, 1 min, or 10 min or greater or less than 10 sec and 10 min. The first operating frequency can be between 0.1 Hz and 100 Hz, such as around 0.1 Hz, 1 Hz, 10 Hz, or 100 Hz or greater or less than 0.1 Hz and 100 Hz. The source of negative pressure can include a piezoelectric pump. The source of negative pressure can be a micropump. The source of negative pressure can be disposed on or within the wound dressing. The driving circuit can include an H-bridge. The controller can provide a control signal to the driving circuit, and the controller can control the electrical current supplied by the driving circuit by adjusting a pulse width modulation of the control signal. The driving circuit can supply an electrical voltage across input terminals of the source of negative pressure via the coupling circuit, and the electrical voltage can range from greater than −50 V to less than +50 V.

Other Variations

Any value of a threshold, limit, duration, etc. provided herein is not intended to be absolute and, thereby, can be approximate. In addition, any threshold, limit, duration, etc. provided herein can be fixed or varied either automatically or by a user. Furthermore, as is used herein relative terminology such as exceeds, greater than, less than, etc. in relation to a reference value is intended to also encompass being equal to the reference value. For example, exceeding a reference value that is positive can encompass being equal to or greater than the reference value. In addition, as is used herein relative terminology such as exceeds, greater than, less than, etc. in relation to a reference value is intended to also encompass an inverse of the disclosed relationship, such as below, less than, greater than, etc. in relations to the reference value. Moreover, although blocks of the various processes may be described in terms of determining whether a value meets or does not meet a particular threshold, the blocks can be similarly understood, for example, in terms of a value (i) being below or above a threshold or (ii) satisfying or not satisfying a threshold.

Features, materials, characteristics, or groups described in conjunction with a particular aspect, embodiment, or example are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract, and drawings), or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features or steps are mutually exclusive. The protection is not restricted to the details of any foregoing embodiments. The protection extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of protection. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made. Those skilled in the art will appreciate that in some embodiments, the actual steps taken in the processes illustrated or disclosed may differ from those shown in the figures. Depending on the embodiment, certain of the steps described above may be removed, others may be added. For example, the actual steps or order of steps taken in the disclosed processes may differ from those shown in the figure. Depending on the embodiment, certain of the steps described above may be removed, others may be added. For instance, the various components illustrated in the figures may be implemented as software or firmware on a processor, controller, ASIC, FPGA, or dedicated hardware. Hardware components, such as processors, ASICs, FPGAs, and the like, can include Iodic circuitry. Furthermore, the features and attributes of the specific embodiments disclosed above may be combined in different ways to form additional embodiments, all of which fall within the scope of the present disclosure.

User interface screens illustrated and described herein can include additional or alternative components. These components can include menus, lists, buttons, text boxes, labels, radio buttons, scroll bars, sliders, checkboxes, combo boxes, status bars, dialog boxes, windows, and the like. User interface screens can include additional or alternative information. Components can be arranged, grouped, displayed in any suitable order.

Although the present disclosure includes certain embodiments, examples and applications, it will be understood by those skilled in the art that the present disclosure extends beyond the specifically disclosed embodiments to other alternative embodiments or uses and obvious modifications and equivalents thereof, including embodiments which do not provide all of the features and advantages set forth herein. Accordingly, the scope of the present disclosure is not intended to be limited by the specific disclosures of preferred embodiments herein, and may be defined by claims as presented herein or as presented in the future.

Conditional language, such as “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements, or steps. Thus, such conditional language is not generally intended to imply that features, elements, or steps are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without user input or prompting, whether these features, elements, or steps are included or are to be performed in any particular embodiment. The terms “comprising,” “including,” “having,” and the like are synonymous and are used inclusively, in an open-ended fashion, and do not exclude additional elements, features, acts, operations, and so forth. Also, the term “or” is used in its inclusive sense (and not in its exclusive sense) so that when used, for example, to connect a list of elements, the term “or” means one, some, or all of the elements in the list. Further, the term “each,” as used herein, in addition to having its ordinary meaning, can mean any subset of a set of elements to which the term “each” is applied.

Conjunctive language such as the phrase “at least one of X, Y, and Z,” unless specifically stated otherwise, is otherwise understood with the context as used in general to convey that an item, term, etc. may be either X, Y, or Z. Thus, such conjunctive language is not generally intended to imply that certain embodiments require the presence of at least one of X, at least one of Y, and at least one of Z.

Language of degree used herein, such as the terms “approximately,” “about,” “generally,” and “substantially” as used herein represent a value, amount, or characteristic close to the stated value, amount, or characteristic that still performs a desired function or achieves a desired result. For example, the terms “approximately”, “about”, “generally,” and “substantially” may refer to an amount that is within less than 10% of, within less than 5% of, within less than 1% of, within less than 0.1% of, and within less than 0.01% of the stated amount. As another example, in certain embodiments, the terms “generally parallel” and “substantially parallel” refer to a value, amount, or characteristic that departs from exactly parallel by less than or equal to 15 degrees, 10 degrees, 5 degrees, 3 degrees, 1 degree, or 0.1 degree.

The scope of the present disclosure is not intended to be limited by the specific disclosures of preferred embodiments in this section or elsewhere in this specification, and may be defined by claims as presented in this section or elsewhere in this specification or as presented in the future. The language of the claims is to be interpreted broadly based on the language employed in the claims and not limited to the examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive. 

1-35. (canceled)
 36. An apparatus for applying negative pressure to a wound, the apparatus comprising: a source of negative pressure configured to provide negative pressure via a fluid flow path to a wound; a driving circuit configured to: generate a driving signal comprising a varying electrical voltage or a varying electrical current, and provide the driving signal to the source of negative pressure to cause the source of negative pressure to provide negative pressure; and a controller programmed to, while the source of negative pressure is providing negative pressure: determine a magnitude of the driving signal at a first time and a magnitude of the driving signal at a second time subsequent to the first time, and vary a frequency at which the driving signal is generated by the driving circuit responsive to a comparison of the magnitude of the driving signal at the first time to the magnitude of the driving signal at the second time.
 37. The apparatus of claim 36, wherein the controller is programmed to determine the magnitude of the driving signal at the first and second times and vary the frequency at which the driving signal is generated by the driving circuit responsive to a detected change in temperature.
 38. The apparatus of claim 36, wherein the controller is programmed to determine the magnitude of the driving signal at the first time and the second time from an electrical current through a resistor connected to the driving circuit.
 39. The apparatus of claim 36, wherein the controller is programmed to: in response to determining that the magnitude of the driving signal at the first time is less than the magnitude of the driving signal at the second time, operate the driving circuit to increase the frequency at which the driving signal is generated by the driving circuit; and in response to determining that the magnitude of the driving signal at the first time is greater than the magnitude of the driving signal at the second time, operate the driving circuit to decrease the frequency at which the driving signal is generated by the driving circuit.
 40. The apparatus of claim 39, wherein the controller is programmed to: operate the driving circuit to increase by a first amount the frequency at which the driving signal is generated by the driving circuit; and operate the driving circuit to decrease by a second amount the frequency at which the driving signal is generated by the driving circuit.
 41. The apparatus of claim 40, wherein the first amount is the same as the second amount.
 42. The apparatus of claim 40, wherein the first amount or the second amount varies over time.
 43. The apparatus of claim 36, wherein the controller is programmed to operate the driving circuit so that the frequency of the driving signal matches an initial frequency when the driving circuit activates the source of negative pressure to begin providing negative pressure, and the controller is programmed to operate the driving circuit to vary the frequency of the driving signal within a first period of time following the driving circuit activating the source of negative pressure.
 44. The apparatus of claim 43, wherein the source of negative pressure has a mechanical resonance frequency, and the mechanical resonance frequency is different than the initial frequency.
 45. The apparatus of claim 36, wherein the controller is programmed to iteratively determine the magnitude of the driving signal and use the magnitude of the driving signal in a first iteration as the magnitude of the driving signal in a second iteration subsequent to the first iteration.
 46. The apparatus of claim 45, wherein the first iteration and the second iteration are not separated by another iteration.
 47. The apparatus of claim 36, wherein the source of negative pressure comprises a piezoelectric pump or a micropump.
 48. The apparatus of claim 36, wherein the driving circuit comprises an H-bridge circuit.
 49. The apparatus of claim 36, further comprising a wound dressing configured to cover the wound, the source of negative pressure being disposed on or within the wound dressing.
 50. A method of operating an apparatus for applying negative pressure to a wound, the method comprising: while a source of negative pressure is providing negative pressure in a fluid flow path connecting the source of negative pressure to a wound: determining a magnitude of a driving signal provided to the source of negative pressure at a first time and a magnitude of the driving signal at a second time subsequent to the first time, wherein the driving signal comprises a varying electrical voltage or a varying electrical current, and varying a frequency of the driving signal responsive to comparing the magnitude of the driving signal at the first time to the magnitude of the driving signal at the second time, wherein the method is performed under control of a controller of the apparatus.
 51. The method of claim 50, wherein determining the magnitude of the driving signal at the first and second times and varying the frequency at which the driving signal is performed responsive to detecting change in temperature.
 52. The method of claim 50, wherein determining the magnitude of the driving signal at the first time and the second time is performed based on monitoring an electrical current through a resistor.
 53. The method of claim 50, further comprising: in response to determining that the magnitude of the driving signal at the first time is less than the magnitude of the driving signal at the second time, causing an increase of the frequency of the driving signal; and in response to determining that the magnitude of the driving signal at the first time is greater than the magnitude of the driving signal at the second time, causing a decrease of the frequency of the driving signal.
 54. The method of claim 50, further comprising iteratively determining the magnitude of the driving signal and using the magnitude of the driving signal in a first iteration as the magnitude of the driving signal in a second iteration subsequent to the first iteration.
 55. The method of claim 54, wherein the first iteration and the second iteration are not separated by another iteration. 